require("rom/apis/rednet")
function lookup(protocol, hostname)
--    expect(1, protocol, "string")
--    expect(2, hostname, "string", "nil")
    -- Build list of host IDs
    local results = nil
    if hostname == nil then
        results = {}
    end
    
    -- Check localhost first
    if hostnames and hostnames[protocol] then
        if hostname == nil then
            table.insert(results, {os.getComputerID(),os.getComputerLabel()})
        elseif hostname == "localhost" or hostname == hostnames[protocol] then
            return {os.getComputerID(),os.getComputerLabel()}
        end
    end
    if not isOpen() then
        if results then
            return results
        end
        return {}
    end

    -- Broadcast a lookup packet
    broadcast({
        sType = "lookup",
        sProtocol = protocol,
        sHostname = hostname,
    }, "dns")
    
    -- Start a timer
    local timer = os.startTimer(0.05)
    -- Wait for events
    while true do
        local event, p1, p2, p3 = os.pullEvent()
        if event == "rednet_message" then
            -- Got a rednet message, check if it's the response to our request
            local sender_id, message, message_protocol = p1, p2, p3
            if message_protocol == "dns" and type(message) == "table" and message.sType == "lookup response" then
                if message.sProtocol == protocol then
                    if hostname == nil then
                        table.insert(results, {sender_id,message.sHostname})
                    elseif message.sHostname == hostname then
                        return {sender_id,message.sHostname}
                    end
                end
            end
        elseif event == "timer" and p1 == timer then
            -- Got a timer event, check it's the end of our timeout
            break
        end
    end
    
    if results then
        return results
    end
    return {}
end
return {lookup = lookup}